1. Field of the Invention
This invention relates generally to communication systems, and, more particularly, to wireless communication systems.
2. Description of the Related Art
Wireless communication systems typically include a geographically dispersed network of base stations or access points for providing wireless connectivity to mobile units. The widespread deployment of wireless networks in buildings provides an opportunity to estimate the location of people and objects in real-time for emergency response, protection of corporate assets, and personalized, location-based communications. However, estimating the location of a roaming mobile unit has proven difficult, particularly for mobile units that do not include Global Positioning System (GPS) functionality. Even mobile units that include GPS functionality may be difficult to locate in some circumstances, e.g., when the mobile unit is inside a building or otherwise unable to acquire the necessary satellite signals. These mobile units may therefore not be able to take advantage of location-based services and it may not be possible to locate these users for emergency response.
One type of indoor tracking system uses a “signal map” of the interior space to locate mobile units within the space. Each mobile unit produces a characteristic pattern of signals when it transmits to the network. Entries in the signal map may therefore include a location in the interior space and a characteristic pattern of signals expected to be produced by a mobile unit transmitting from this location. The signal map is indexed by the signal patterns, which can be matched to the received signals. Under reasonable assumptions concerning the signals, the signal map can be employed to locate users within the building. For example, signals from a tracked user can be matched to the entries in the signal map and the entry in signal space closest to the measured signals is taken to determine the location. This method of locating a mobile unit is typically called finger printing or pattern matching.
The conventional fingerprinting method of determining a mobile unit location requires that the signal map be developed manually before attempting to locate any mobile units. One technique for developing a signal map is to have a test user move around the building, make signal measurements at multiple points, and record the location at which each set of measurements is made, i.e. the data includes a signal value that is labeled with the location of the mobile unit used to make the measurement. This approach is time-consuming and laborious because hundreds or even thousands of locations may be involved. Furthermore, the map is expected to be in a constant state of change due to changes in the environment, changes in the location and/or number of access points, and the like. Maintaining the signal map as the signal environment changes requires constant vigilance and regular repetition of the time-consuming and laborious data gathering process used to acquire the labeled location data and create the signal map in the first place.
A second potential solution is to deploy a network of sensors throughout the interior space at known locations. The sensor network would constantly monitor the locating signals and relay them to a central database. The signal data is therefore automatically labeled with the fixed locations of the sensors and so the central database can use the labeled information to maintain the signal map. This procedure relies on costly hardware as well as careful selection of locations to generate the labeled data required to form an accurate map. This approach also requires deployment of a sufficiently large number of sensors to maintain the signal map so that it provides sufficient location accuracy.